The present invention relates to transducer head assemblies for rotating disk drives, and more particularly to air bearing disk head sliders for use with rotary actuators.
Transducer head assemblies that "fly" relative to a rotating disk are used extensively in rotating disk drives. The assemblies include an air bearing slider for carrying a magnetic transducer proximate the rotating disk. FIG. 1 illustrates a slider 10 supported by a gimbal 11 over a disk 14. The gimbal 11 is secured to an arm 12. The arm 12 positions the slider 10 over individual data tracks on the disk 14 (not shown) along an arc 18. As the disk 14 rotates, it generates wind or air flow in the direction shown by arrows 16 (wind 16). The wind 16 is approximately parallel to the disk's tangential velocity, indicated by an arrow 22. The wind cooperates with the slider 10 to provide lift which allows the slider to fly above the disk 14.
The gimbal 11 is a resilient spring that allows the slider 10 to follow the topography of the disk 14. The gimbal 11 includes a dimple (not shown) that is in point contact with the slider 10. The dimple provides a pivot about which the slider 10 can pitch and roll while following the topography of the disk 14.
When the slider 10 is positioned near the outside edge of the disk 14, its longitudinal axis 20 is substantially parallel to the wind direction. Near the center of the disk 14, the slider 10 is skewed with respect to the wind direction as illustrated by a skew angle .phi.. The skew angle .phi. is measured between the longitudinal axis 20 and the wind 16.
The elements described to this point may be conventional in design and are described and shown in FIGS. 1 and 2a-2e to facilitate an understanding of the present invention. Throughout the FIGS., elements of the same design are designated by identical reference numerals.
FIG. 2a is a perspective view of a head-gimbal assembly having a conventional catamaran slider 30. The slider 30 is secured to the gimbal 11 in any known manner. The slider 30 and the gimbal 11 are supported by the arm 12. Rails 32 and 34, positioned along edges of the slider 30, form air bearing surfaces on which the slider flies, in known manner.
FIG. 2b is an end view of the slider 30 as seen from line 2B--2B of FIG. 2a. The arm 12 and the gimbal 11 support the slider 30 above the disk 14. The slider 30 includes the rails 32 and 34 which carry transducers 35 and 37. The rails 32 and 34 include air bearing surfaces 38 and 39 which provide lift to the slider 30, as described more fully below.
Flying height is viewed as one of the most critical parameters of non-contact recording. As the average flying height of the slider 30 decreases, the transducers 35 and 37 achieve greater resolution between individual data bit locations on the disk 14. Therefore, it is desirable to have the transducers 35 and 37 fly as close to the disk 14 as possible.
FIG. 2c is a bottom plan view of the conventional catamaran slider 30 shown in FIGS. 2a and 2b. The rails 32 and 34 are positioned along edges of the slider 30 and are disposed about a recessed area 36 to form the air bearing surfaces 38 and 39. As the disk 14 rotates, the disk drags air (wind 16) under the slider 30 and along the air bearing surfaces 38 and 39. Under the air bearing surfaces 38 and 39, the air flow component due to the drag of the disk 14 is called "couette flow". As couette flow passes beneath the rails 32 and 34, the skin friction on the air bearing surfaces 38 and 39 causes the air pressure between the disk 14 and the air bearing surfaces to increase and to thereby provide lift causing the slider 30 to fly above the disk surface. Hence, the greater the air bearing surface area, the greater the lift.
The flying height is preferably uniform regardless of variable flying conditions, such as tangential velocity variation from inside to outside tracks, lateral slider movement during a seek, and varying skew angles .phi.. Catamaran sliders provide just enough air bearing surface area to fly at a proper height above the disk surface. For example, without the rails 32 and 34, the air bearing surface area would be too large. Consequently, the slider 30 would fly too far from the disk surface at a height adversely affecting resolution.
Although, conventional catamaran sliders are helpful in controlling flying height, they are very sensitive to skew angle .phi.. Even with moderate skew angles in the 10-15 degree range, flying height for a conventional catamaran slider is adversely influenced. Increasing skew angle .phi. at a fixed tangential velocity causes the air pressure distribution beneath the rails 32 and 34 to become distorted. This influences the net forces and torque acting upon the slider 30 and results in decreased flying height.
FIG. 2d is a bottom view of the rail 32 with the wind 16 applied at zero skew. The air bearing surface 38 has an effective area 40 at zero skew which is equal to the area of the air bearing surface 38. FIG. 2e illustrates the wind 16 applied to the rail 32 at skew angle .phi.. The air bearing surface 38 now has a smaller effective area 41. As the skew angle .phi. increases, the effective surface area of the rails 32 and 34 decreases. The decrease of effective surface area at skew is caused by side leakage. The air that leaks out the sides of the rails 32 and 34 is not available to generate pressure under the rails. This causes a loss of pressure beneath the rails 32 and 34 resulting in a lower flying height at greater skew. To prevent the slider 30 from ultimately contacting the disk surface at large skew angles, the slider's average flying height must be appropriately increased. Resolution is therefore sacrificed. Further, the pressurization of one rail may differ from the pressurization of the other rail at skew. This difference causes the slider 30 to roll. In other words, the rail 32 will fly at a different height than the rail 34 while the slider 30 flies at skew.
As disk drives become more compact for applications in smaller and more portable equipment, rotary actuators are increasingly employed. Further, the designer is motivated to use a shorter actuator pivot arm to make the disk drive even more compact. However, these actuators create rather large skew angles .phi. and consequently make flying height control more difficult. Rotary actuators cause the geometric orientation between longitudinal axis 20 (shown in FIG. 1) and the disk rotation tangent, to change as the arm 12 moves the slider 10 along the arc 18.
One approach to reducing sensitivity of the flying characteristics to varying skew angles is to provide edge blends extending along the length of each rail. As early as 1982, designers applied these blends to reduce wear caused by contact between each rail and the disk surface. The edge blends also reduced sensitivity of the flying characteristics to varying skew angles created by rotary actuators. For example, the pressurization distribution on each rail remained nearly constant relative to the slider's pivot point over varying skew angles. The benefits to flying characteristics became known in 1982 when the edge blends were used in combination with rotary actuators in 51/4 inch disk drives, such as the WREN family manufactured by IMPRIMIS Technology, Inc.
White U.S. Pat. No. 4,693,996 discloses a similar approach. The White patent shows transverse pressurization contours (TPC) on each rail that extend from the leading edges to the trailing edges. The TPCs provide a pressurization region across one side edge of each rail and a depressurization region across the opposite side edge such that the pressure distributions across the air bearing surfaces are substantially unaltered over varying skew angles.